A research plan is proposed which is based on designing and maintaining a large clinical database, to be used as an "assessment core" that will include diagnostic and medication assessment data. Over the course of five years, several studies will be conducted using only the data from the assessment core, but several other studies will be conducted by either adding measures to the core or by recruiting subjects who have participated in assessment for other studies (thereby obviating the need for re-assessment). An initial study of Cloninger's tridimensional theory, as applied to child disruptive behavior disorders, is planned.